Fig. 4

Potential-dependent ¹⁸O KIEs for the OER at nanoporous Fe₂O₃ or Ir electrodes. ¹⁸O KIEs of nanoporous Fe₂O₃ (blue data points) or Ir (green data points) are presented for different applied overpotentials η. Steady-state electrolyses were performed in a 0.1 M KH₂PO₄ solution (pH neutral) for 3 h or in a 0.1 M H₂SO₄ solution for 0.5 h at Fe₂O₃ and Ir electrodes, respectively. The ¹⁸O KIEs presented are average values calculated from three nominally identical individual samples. Their corresponding standard deviations are shown as error bars. The unity KIE value is indicated by the dashed line